Continuing efforts exist to make fabrics that will be converted into garments (also referred to as equipment), e.g. jackets, rucksacks, ballistic vests, boots, etc. that are substantially invisible in near infrared wavelengths. To do this, the fabric/garment must closely match the NIR signature of the surroundings. Each terrain element has a different reflective signature based on its chemical make-up. For example, foliage (a major component of woodland environments) has a relatively low reflectance in the visible region and a relatively high reflectance in the NIR region. In contrast, sand, a major component of desert environments, and concrete, a major component of urban environments, have a relatively high reflectance in the visible region and a low reflectance in the NIR region. It is well known that polyamide and polyester fibers are very reflective in the 400–2000 nm range. It is desirable to reduce NIR reflectance of polyamide and polyester garments and equipment so that they closely match the NIR reflectance of the environment and are therefore not revealed by the use of night vision devices, such as night vision goggles or image intensified converters.
Techniques to provide near-infrared (NIR) camouflage for dark colors are known in the art. For example, NIR camouflage garments having military solid color olive drab and woodland prints are obtainable through the use of pigmented yarns or by dying yarns using so-called pre-metallized dyes. However, durable garments made from other polymer fibers, such as polyamide fibers, may not exhibit satisfactory dye levelness resulting in higher reflectance than desired in the NIR for olive drab and woodland patterns. Light colored garments such as solid tan (e.g. the color of common desert or beach sand), desert camouflage or more specifically the “U.S. Army 3-day desert print” do not meet NIR reflectance specifications for military applications. As a result, these lightly colored polymeric materials are easily seen with the aid of night vision goggles, especially in the range of 600 to 900 nm.
Known methods to reduce infrared (IR) reflectance of fabrics use IR absorbing pigments in combination with the fabric. For example; U.S. Pat. No. 5,798,304 to Clarkson (“Clarkson”), the disclosure of which is hereby incorporated by reference, discloses that carbon black pigment absorbs light in the IR range 1000 to 1200 nm. Clarkson discloses a fabric that comprises a camouflage pattern, where the camouflage pattern is visible in the IR region but is invisible in the visible region. The fabric may be printed with a non-camouflage pattern that is visible in the visible region of the spectrum. To achieve this, Clarkson prints the fabric with an IR-absorbing material, such as carbon black, a chitin resin or other IR-absorbing pigment. Clarkson discloses that the IR-reflectivity of the fabrics is arranged to match that of the surroundings in which it is to be used. For example, Clarkson discloses that for temperate foliage overall IR reflectivity is typically required to be 35%, which may rise to 70% for desert regions. To achieve the desired overall reflectivity, the camouflage pattern comprises at least two areas of different IR-reflectivity which differ by at least 5%. The IR-camouflage pattern is generally printed onto the fabric after the fabric has been dyed.
U.S. Pat. No. 4,095,940 to Weingarten (“Weingarten”), the disclosure of which is hereby incorporated by reference, discloses a process for producing camouflage dyeing and prints on synthetic or regenerated fibers to obtain dyed materials having camouflage properties in the visible and IR regions. Weingarten reports dyed materials having reflection values of from 20 to 50% in the IR spectrum from 700 to 1100 nm produced by spun-dying fibers with carbon black. For example, Weingarten discloses that spun-dyed polyester rayon comprising 0.02 weight % carbon black alters the IR reflection curve of the fabric but it does not show the required steep increase of the reflection values at about 700 nm characteristic of chlorophyll. Weingarten discloses that the use of carbon black as a mass coloration in the range of 0.005 to 0.5 weight % in synthetic fibers or foils in combination with cross-dyeing can produce IR reflection values of from 20 to 50% between 700 and 1100 nm while only slightly altering the shade of the fabric in the visible wave range. The spun-dyed material alone; without cross-dyeing, did not achieve reflectance values of 5 to 35% at 700 nm; 30 to 50% at 800 nm; and values neither higher nor lower than these values up to 1100 nm. All examples in Weingarten that displayed desirable reflectance values were cross-dyed to a green, olive, green-olive or bluish-green shade.